As one type of the negative pressure-type booster device, one described in Patent Literature 1 is known. As shown in FIG. 4 in Patent Literature 1, in the negative pressure-type booster device, a control valve includes a control valve 61 biased by a spring 60 toward a valve plunger 42, a sheet plane 151e of a power piston 151, and an atmospheric-pressure control sheet part 421a disposed at a rear end of a first valve plunger 421. The atmospheric-pressure control sheet part 421a has an approximately semispherical shape, and the center of the approximately semispherical atmospheric-pressure control sheet part 421a decenters in a direction orthogonal to the axis line of the valve plunger 42. The decentering of the center of the approximately semispherical atmospheric-pressure control sheet part 421a allows a lower part of a seal plane 611 and a lower part of the sheet plane 151e to be in contact with each other in an inactive state.
In this manner, the approximately semispherical atmospheric-pressure control sheet part 421a shortens a moving distance of a push rod 41 to the left on the drawing plane with respect to the power piston 151 from the inactive state to the active state of the negative pressure-type booster device to improve a brake feeling.